Sports medicine is now looking into a new twist on this proven technique by studying a theory known as "train low and compete high". This new training theory is built on the premise of periodically training with low glycogen stores, which is a complete change from what we've always been taught.
Athletes who have a diet based on carbohydrates have no lack of glycogen stores in their body and are able to compete at higher levels and for longer periods of time. This technique has been used successfully for over fifty years and is called the "train high compete high" method. This method works because it is based on the sound principle that both carbohydrates and fat are needed to generate the energy needed during exercise. When doing endurance exercises at a moderate pace, approximately 50% to 60% of the energy needed will come from carbohydrates and the rest will come from fat. The more you push yourself the more you will rely on the carbs. The problem comes when you have to rely on your reserve carbohydrates, which come from the glucose in your blood stream and the glycogen that is in your muscles and liver. This is why it is so important that you take in the necessary amount of glycogen prior to beginning any type of endurance exercises. When your muscle glycogen stores become low, you effectively run out of energy or "hit the wall". When this reserve runs low your blood sugar level drops and you're pretty much running on an empty tank. Your body is no longer using the fast burning carbohydrates you consumed, and the slower burning fat reserves can't be metabolised fast enough.
Scientists are trying to determine if body fat can also be used as an energy source, and if an athlete can perform in a low glycogen state. Scientists and researchers in Denmark conducted a study using a group of men performing leg extension exercises. They performed these exercises five days a week for 10 weeks while taking in predominantly carbohydrates in their diet. One leg was worked out every day in a one-hour session while the other leg was exercised every other day in a two-hour session. The workout load was the same for each leg, but one leg was in a glycogen-depleted state while the other was "carbohydrate loaded".
Ten weeks later the research showed that both legs were just as strong but the leg that was exercised in a low glycogen state was able to work out twice as long as the leg that had higher levels of glycogen. The reason is that the body saw the low glycogen leg as a temporary state and began to burn fat as a fuel. This study was conducted with men who were not trained or performance athletes. In addition, the leg extension exercises did not effectively imitate whole body exercises that would put more of a strain on our glycogen reserves, such as bicycling or marathon running.
Then scientists conducted the same test using trained cyclists and triathletes performing as they normally would. The results of this study showed there was no increased in performance while in a low glycogen state. Additionally, athletes performing high intensity exercises while in a low glycogen state showed a decrease in their performance. Scientists have now concluded that more research is needed to fully determine whether or not there benefits of "training low" for athletes of all competitive levels. It has been known for many years that some athletes, bodybuilders included, say that they begin their morning workouts on an empty stomach and have no problems with their energy levels. In fact some African marathon runners have been known to do their training early in the morning while their bodies are in a fasting state from the day before.
The conclusion regarding low glycogen training is that it does allow your body to utilise fat as an energy source when exercising. Unfortunately in the area of performance there are no added benefits, and this is ultimately what would make this training technique something to be adopted. Until further research is done low glycogen training, it may work for some but the rule of thumb is to take in plenty of carbohydrates prior to any high-intensity or endurance exercise to ensure that you have the proper fuel for your activity.